Efficacy of One or Two Doses of Ty21a Salmonella Typhi Vaccine in Enteric-Coated Capsules in a Controlled Field Trial. Chilean Typhoid Committee

Vaccine. 1990 Feb;8(1):81-4. doi: 10.1016/0264-410x(90)90183-m.


Typhoid fever remains an important public health problem in many areas of the world and an effective, non-reactogenic vaccine would be useful to control this disease. An attenuated Salmonella typhi strain (Ty21a), which has shown promise in previous trials, was evaluated in a controlled field trial in Santiago, Chile. In this trial, 82,543 schoolchildren were randomly assigned to receive one or two doses of Ty21a vaccine in enteric-coated capsules or placebo. The enteric-coated vaccine formulation was well tolerated and practical for mass oral immunization. In the first two years of surveillance, 213 cases of bacteriologically-confirmed typhoid fever were found in schoolchildren participating in the trial; annual rates in the placebo group were 139 and 227 per 100,000. Vaccine efficacy in the first two years after vaccination was 59% for two doses and 29% for one dose; no efficacy was found 3-5 years after vaccination. These results indicate that it will be necessary to identify a vaccine formulation and schedule for Ty21a S. typhi that is practical and provides high level protection for greater than 2 years.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Administration, Oral
  • Adolescent
  • Adult
  • Child
  • Dose-Response Relationship, Immunologic
  • Double-Blind Method
  • Humans
  • Immunization Schedule
  • Randomized Controlled Trials as Topic
  • Salmonella typhi / immunology*
  • Typhoid Fever / prevention & control*
  • Typhoid-Paratyphoid Vaccines* / administration & dosage
  • Vaccines, Attenuated / administration & dosage


  • Typhoid-Paratyphoid Vaccines
  • Vaccines, Attenuated